This invention relates generally to improvements in compact hot water heaters, particularly of the gas-fired type used in recreational vehicles and the like to provide a portable supply of hot water. More particularly, this invention relates to an improved compact water heater for recreational vehicles and the like, wherein the water heater is designed for rapid, cost-efficient assembly with improved heat transfer for faster heater recovery times.
Compact water heaters of the type for use with recreational vehicles and the like are generally well known in the art and typically comprise a relatively small water tank in combination with an internal heating element conventionally of the gas-fired type. The water heater is mounted on the recreational vehicle in a convenient position connected to cold water supply and hot water outlet pipes respectively receiving cold water from a suitable water supply source and for directing heated water, normally at about 120.degree. F. to 170.degree. F., for use in cooking, bathing, and the like. In a standard commercially available water heater for recreational vehicles, the tank has a cylindrical shape about sixteen inches in length and about twelve inches in diameter, and has a capacity of about six gallons of water to be heated. The heater is normally mounted on the vehicle for convenient access through a hinged door or the like to selected control components including, for example, a thermostatic gas flow control valve, a pressure relief valve, drain plug, etc.
In the past, the desired compact size of the water tank used in recreational vehicle water heaters has placed significant design constraints upon the heating element extending into the tank for heating the water. More particularly, bent tube combustor elements have been used wherein a length of metal tubing bent to a generally U-shaped configuration is installed within the tank to define a generally U-shaped flow path extending in one direction into and then exiting in an opposite direction from the tank. Such bent tube structures have been limited to tubes of round cross sectional shape to provide a heating element capable of withstanding a typical tank pressure test at about 300 psi. A burner element is mounted near one open end of this bent tube flow path to create hot combustion products which travel through and are exhausted from the flow path, with a resultant heat transfer exchange with water in the tank. However, the compact tank profile significantly restricts the diametric size of the bent tubing which can be installed into the tank. This results in corresponding limmitations in tank heat transfer capacity, with a typical commercially available water heater of this type having a maximum heat transfer capacity of about 12,200 BTU's per hour.
Alternative combustor element configurations have included comparatively larger diameter straight tubes having one closed end and an internal median divider to define hemispherical flow paths extending into an exhausting from the tank. However, once again, this type of combustor element provides relatively limited heat transfer surface area with surrounding water in the tank to correspondingly limit the heat transfer capacity of the tank. Enhanced heat transfer capacity, of course, is extremely desirable since it would permit supply of increased quantities of hot water per hour, without increasing the size of the water heater.
There exists, therefore, a significant need for improvements in compact water heaters of the type designed, for example, for recreational vehicles and the like. In particular, there exists a need for an improved water heater having increased heat transfer capacity without increasing overall heater size, wherein an internal heating element for the water heater is easily assembled, provides substantial heat transfer surface area, and is capable of withstanding design pressure tests up to 300 psi. The present invention fulfills these needs and provides further related advantages.